Extra-oral anchorage and traction have been of invaluable aid in the treatment of dental malocclusions, and were first reported as being used in the treatment of maxillary protrusions in the 1880's. Changes wherein the extra-oral forces have aided in remodeling the maxillae and maxillary dentition have been amply demonstrated.
One of the most commonly used appliances has been the so-called Kloehn face bow, named after its originator, S.J. Kloehn. The Kloehn face bow and variations thereof, such as those shown in U.S. Pats. Nos. 721,655, 3,036,380, 3,111,758, 3,137,841, 3,311,978, 3,314,151 and 3,429,044, all utilize an inner bow which is either welded or otherwise affixed to an outer bow in a manner such that the two bows cannot be readily separated when the outer bow is pulled
As a result thereof, there have been a number of serious injuries reported, as where someone, such as a playmate, has playfully grabbed the outer bow and pulled it forward to such an extent that the free ends of the inner bow were completely removed from the mouth. Then, under the tension from the elastic in the high-pull headgear, the outer bow slipped out of the playmate's grasp and the pointed ends of the inner bow were driven into both of the patient's eyes, resulting in total blindness.